Scroll sideways with Shift or Alt and the wheel, and in the outline

A wheel that tilts (or a touchpad) already panned the canvas sideways,
but only when the terminal passes those events on, and many don't:
Windows Terminal only does since 1.24, and Windows' own console layer
can drop them. The wheel with Shift held now scrolls sideways too, as in
most apps, and so does Alt, since Alacritty and Windows Terminal keep
Shift with the mouse for selecting text.

The outline scrolls sideways as well (the wheel, zh and zl), for rows
wider than its pane: a deep tree or a long title. Clicks land where the
rows are, however far they're scrolled, and when the cursor moves its
title comes back into view.

Fixed on the way: the wheel turned sideways over the help, the menu, a
picker or the K card moved it up.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

DESIGN.md

@@ -154,6 +154,8 @@ lines.
   title, where its children hang, to read the document like a page. `j` and
   `k` go row by row, `h` and `l` to the parent and the first child; a click
   on a marker folds. Titles are edited in their row, rapid entry included.
+  Rows wider than the view scroll sideways (`zh` `zl`, the wheel sideways),
+  and the cursor's title comes back into view when the cursor moves.
 - Move mode in the outline and the Note view moves the node through the
   tree: `j` and `k` swap it with its siblings (`J` and `K` five places), `h`
   takes it out a level, `l` puts it under the one above.
@@ -313,8 +315,10 @@ backlinks, and the backlink paths in every document it points to.
 
 **Mouse** (on the canvas; other views get click, double-click and scroll):
 click selects, double-click edits the title (from the letter clicked),
-dragging a node moves it with its branch, dragging empty space pans, scrolling
-pans, Ctrl+drag selects a rectangle, Ctrl+click adds or removes one node,
+dragging a node moves it with its branch, dragging empty space pans, the wheel
+pans up and down, and sideways with a wheel that tilts, a touchpad, or the
+wheel with Shift or Alt held (Alt for terminals that keep Shift for selecting
+text), Ctrl+drag selects a rectangle, Ctrl+click adds or removes one node,
 right-click opens a menu built from the same actions as the keys. Zoom is on
 the `+` and `-` keys.